ABSTRACT: Injury associated with sport and recreation is a leading reason for physical activity cessation, which is linked with significant long-term negative consequences. Lateral ankle sprains are the most common injuries associated with physical activity and at least 40% of individuals who sprain their ankle will go on to develop chronic ankle instability (CAI), a multifaceted condition linked with life-long residual symptoms and post- traumatic ankle osteoarthritis. Our long term goal is to develop intervention strategies to decrease disability associated with acute and chronic ankle injury and prevent posttraumatic ankle osteoarthritis. Conventional rehabilitation strategies, are only moderately successful because they ignore the full spectrum of residual symptoms associated with CAI. Manual therapies such as ankle joint mobilizations and plantar massage target sensory pathways not addressed by conventional treatments and have been shown to improve patient- reported outcomes, dorsiflexion range of motion, and postural control in CAI patients. While these early results are promising, the underlying neuromuscular mechanisms of these manual therapies remain unknown. Therefore the objective of this R21 proposal is to determine the neuromuscular mechanisms underlying the improvements observed following independent ankle joint mobilization and plantar massage interventions in CAI patients. To comprehensively evaluate the neuromuscular mechanisms of the experimental treatments, baseline assessments of peripheral (ankle joint proprioception, light-touch detection thresholds, spinal (H- Reflex of the soleus and fibularis longus), and supraspinal mechanisms (cortical activation, cortical excitability, and cortical mapping, sensory organization) will be assessed. Participants will then be randomly assigned to receive ankle joint mobilizations (n=20), plantar massage (n=20), or a control intervention (n=20) which will consist of 6, 5-minute treatments over 2-weeks. Post-intervention assessments will be completed within 48- hours of the final treatment session. Separate ANOVAs will assess the effects of treatment group (ankle joint mobilization, plantar massage, control) and time (baseline, post-treatment) on peripheral, spinal, and supraspinal neuromuscular mechanisms in CAI participants. Associations among neuromuscular mechanisms and secondary measures (biomechanics and postural control) will also be assessed. The results of this investigation will elucidate multifaceted mechanisms of novel and effective manual therapies (ankle joint mobilizations and plantar massage) in those with CAI.